A semiconductor device having an IGBT element used in an electronic apparatus such as an industrial motor has been known as a semiconductor power conversion device. It has been proposed to reduce a surge voltage at the time of turn-off in this type of semiconductor device (for example, refer to a patent document 1).
For example, in a trench gate IGBT element, an N−-type drift later is formed on a P+-type collector layer, and a P-type base layer is formed in a surface portion of the drift layer. Then, an N+-type emitter layer is formed in a surface portion of the base layer. Further, multiple trenches which reach the drift layer by penetrating the base layer and the emitter layer are formed in a pattern of stripes. A gate insulation layer and a gate electrode are formed in order on a wall of each trench so that a trench gate structure can be formed with the trench, the gate insulation layer, and the gate electrode. Further, an emitter electrode is formed on the base layer and the emitter layer through an interlayer dielectric film. The emitter electrode is electrically connected to the base layer and the emitter layer through a contact hole formed in the interlayer dielectric film. Further, a collector electrode is formed on a back side of a collector layer and electrically connected to the collector layer.
In the semiconductor device having the IGBT element, a predetermined voltage is applied to a part of the gate electrodes through a first resistor and applied to a remainder of the gate electrodes through a second resistor having a resistance smaller than that of the first resistor.
Thus, when the IGBT element is turned off, a turn-off voltage is applied to the part of the gate electrodes through the first resistor while applied to the remainder of the gate electrodes through the second resistor. Therefore, a gate voltage of the remainder of the gate electrodes decreases faster than a gate voltage of the part of the gate electrodes.
For this reason, before the gate voltage of the part of the gate electrodes becomes smaller than a threshold voltage (hereinafter simply referred to as the threshold voltage) of the gate of a MOS, the gate voltage of the remainder of the gate electrodes can become smaller than the threshold voltage. Accordingly, a collector current can be reduced in advance. Then, when the gate voltage of the part of the gate electrodes becomes smaller than the threshold voltage, the collector current becomes zero, and the IGBT element is turned off. That is, the collector current can be reduced stepwise by causing the gate voltage of each gate electrode to be smaller than the threshold voltage at a different time. Thus, a magnitude of the surge voltage can be reduced as compared to when the gate voltage of each electrode is caused to be smaller than the threshold voltage at a time.